<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>第一个javascript计算页面</title>
</head>
<body>
<script type="text/javascript">
var v1=null;
var v2=NaN;
var v3=undefined;
alert(typeof v1);//object
alert(typeof v2);//number
alert(typeof v3);//undefined
alert(v1===v2);//false
alert(v2===v3);//flase
alert(v1===v3);//false
alert(v1==v2);//false
alert(v1==v3);//true
alert(v2==v3);//false
</script>
</html>
原文：https://www.cnblogs.com/god1/p/12114288.html